Clim. Past Discuss., 6, 1853-1894, 2010
www.clim-past-discuss.net/6/1853/2010/
doi:10.5194/cpd-6-1853-2010
© Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 License.
Review Status
This discussion paper has been under review for the journal Climate of the Past (CP). Please refer to the corresponding final paper in CP.
Initiation of a Marinoan Snowball Earth in a state-of-the-art atmosphere-ocean general circulation model
A. Voigt1,2, D. S. Abbot3, R. T. Pierrehumbert3, and J. Marotzke1
1Max Planck Institute for Meteorology, Hamburg, Germany
2International Max Planck Research School on Earth System Modelling, Hamburg, Germany
3Department of Geophysical Sciences, University of Chicago, Chicago, Illinois, USA

Abstract. We study the initiation of a Marinoan Snowball Earth (635 million years before present) with the most sophisticated atmosphere-ocean general circulation model ever used for this purpose, ECHAM5/MPI-OM. A comparison with a pre-industrial control climate shows that the change of surface boundary conditions from present-day to Marinoan, including a shift of continents to low latitudes, induces a global mean cooling of 4.6 K. Two thirds of this cooling can be attributed to increased planetary albedo, the remaining one third to a weaker greenhouse effect. The Marinoan Snowball Earth bifurcation point for pre-industrial atmospheric carbon dioxide is between 95.5 and 96% of the present-day total solar irradiance (TSI), whereas a previous study with the same model found that it was between 91 and 94% for present-day surface boundary conditions. A Snowball Earth for TSI set to its Marinoan value (94% of the present-day TSI) is prevented by quadrupling carbon dioxide with respect to its pre-industrial level. A zero-dimensional energy balance model is used to predict the Snowball Earth bifurcation point from only the equilibrium global mean ocean potential temperature for present-day TSI. We do not find stable states with sea-ice cover above 55%, and land conditions are such that glaciers could not grow with sea-ice cover of 55%. Therefore, none of our simulations qualifies as a "slushball" solution. In summary, our results contradict previous claims that Snowball Earth initiation would require "extreme" forcings.

Citation: Voigt, A., Abbot, D. S., Pierrehumbert, R. T., and Marotzke, J.: Initiation of a Marinoan Snowball Earth in a state-of-the-art atmosphere-ocean general circulation model, Clim. Past Discuss., 6, 1853-1894, doi:10.5194/cpd-6-1853-2010, 2010.
 
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